Study on the methods for detecting AmpC β-lactamase produced by Enterobacter cloacae

Objective To evaluate three methods for detecting AmpC β-lactamase produced by Enterobacter cloacae. Methods Three-dimensional test, improved three-dimensional test and phenotype screening test were performed to detect the 58 strains of Enterobacter cloacae with decreased susceptibilities to the third-generation cephalosporins or aztreonam. The ampD genes from 11 isolates were sequenced. Results From the 58 strains of Enterobacter cloacae, the derepressed AmpC β-lactamase-producers were 70.69% by three-dimensional test, 65.52% by improved three-dimensional test and 86.21% by phenotype screening test respectively. The ampD gene sequencing results of 8 strains which stably producing derepressed AmpC β-lactamase showed that there were amino acid substitutions in the carboxy-terminal of AmpD. Conclusions Phenotype screening test is reliable to detect AmpC β-lactamase and easy to use in department of microbiology.